Long-Path Infrared Spectrocopy for Air Pollution Research

Abstract

A long-path absorption cell was developed for the measurement of gaseous contaminants in the atmosphere and for the studies of reactions of contaminants in the laboratory The instrument is based on the White multiple-reflection system, having two large spherical mirrors at one end of the 3-meter cell and one smaller one at the other end of equal radius. To avoid excessive loss of radiant energy, the infrared source image is magnified and demagnified to match the cell to the spectrometer Optimum path-length for maximum signal is reached when reflection losses reduce the energy to 1/e of its initial value. CO₂ and water vapor interfere with, but do not prohibit, useful analyses of the atmosphere Two of these cells are in use, one in the Philadelphia laboratory and one in a field-study trailer in the Los Angeles area